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Jabiru EI pick up

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Peter H

Joined: 20 Mar 2007
Posts: 197

Posted: Wed May 09, 2007 10:09 pm Post subject: Jabiru EI pick up

Hi again,  

I have been experimenting with an inductive pick up mounted in place of one of the magneto coils on the Jab 3300 and can produce a big fat spark at hand propping speed using a simple electronic ignition module and an automotive coil feeding the Jab distributor. (I suspect the original Jab magnetos were intended to drive just one plug not six through a distributor.) I have been able to increase plug gap to 1.0mm and cold starting is solved plus better spark through the power range. The signal from this sensor is about 4 VAC at idle.  

But at the higher power settings there is a problem caused by the pick up sometimes firing in advance maybe from the leading edge of the three fly wheel magnets. These magnets are also each divided into 3 segments with an 1/8” air gap between them. The end result is spurious unwanted firing. (Only the advanced firing can be detected in flight but it may be firing off the air gaps as well.) Of course the flywheel magnets are meant to excite a magneto not an inductive sensor, but if it can be made to work it is a very simple and effective improvement to ignition.   

I have run the system using the original magneto primary as a signal source for the ignition module but the advantage of a big spark with small movements is lost. (The magneto primary has a transistor which will fire only when primary voltage reaches a set limit at about 270 rpm.)  

It can be solved by increasing the gap clearance to as much as 12mm but then the advantage of hand propping is lost. Although cold starting is still fine I am wondering if the power spark is as good as it could be at this gap setting..  

At this stage I have removed the magnet from the inductive pick up and fitted a steel shield across the span of the magnets at the installation and still getting a very strong signal but still have the unwanted firing. I have no access to an oscilloscope.  

Next experiment will be with the use of diodes in the signal leads.  

But does anyone have a suggestion how to solve this ? I will want to use the pickup for the EFI conversion later.  

Thanks  

Peter    

   

        [quote][b]

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matronics(at)rtist.nl
Guest

Posted: Thu May 10, 2007 1:07 am Post subject: Jabiru EI pick up

Peter,

  

 It sounds like you made your pick up too sensitive.  Maybe it fires because other parts of the flywheel are lightly magnetized and  cause early peaks. When you induce current in a coil, the signal will always  show some oscillations. This is the hard part, getting it 'just right'. you  probably do want to get an oscilloscope to watch the signal shape, so you can  see what unwanted peaks exist, and maybe engineer a dampening circuit that gets  rid of them. Nobody said it would be easy...

  

 Rob

 [quote]   ---

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nuckollsr(at)cox.net
Guest

Posted: Thu May 10, 2007 6:43 am Post subject: Jabiru EI pick up

At 11:02 AM 5/10/2007 +0200, you wrote:



[quote]"urn:schemas-microsoft-com:office:office" xmlns:w = 

"urn:schemas-microsoft-com:office:word">

Peter,



It sounds like you made your pick up too sensitive. Maybe it fires because 

other parts of the flywheel are lightly magnetized and cause early peaks. 

When you induce current in a coil, the signal will always show some 

oscillations. This is the hard part, getting it 'just right'. you probably 

do want to get an oscilloscope to watch the signal shape, so you can see 

what unwanted peaks exist, and maybe engineer a dampening circuit that 

gets rid of them. Nobody said it would be easy...



Rob

---

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Peter H

Joined: 20 Mar 2007
Posts: 197

Posted: Thu May 10, 2007 1:12 pm Post subject: Jabiru EI pick up

Thanks Bob, your explanation ties in exactly with what is happening and

thanks for the clues to solve it . I will list again when fixed.

Peter



--

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